JP2002234320A - Tire air pressure detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a tire air pressure drop accurately even under small dispersion in driving force. SOLUTION: If any dispersion is detected in wheel driving force, a wheel speed deviation value D is corrected according to a currently computed slip deviation value A, and if no dispersion is detected in wheel driving force., the wheel speed deviation value D is corrected according to a previously computed slip deviation value A*. Even under small deviation in driving force, regression accuracy is protected against degradation by a slight disturbance such as a slight turn, a rotational state value can be corrected accurately and a tire air pressure drop can be detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tire pressure detecting device for detecting the state of tire pressure in a vehicle.

[0001]

2. Description of the Related Art As a conventional tire air pressure detecting device, there is one disclosed in Japanese Patent Application Laid-Open No. Hei 10-100624. The tire pressure detecting device disclosed in this conventional publication will be described.

The tire pressure detecting device disclosed in the prior art detects a decrease in tire pressure based on a relationship between a wheel speed deviation value D and a front and rear wheel speed ratio β shown as follows.

[0003]

(Equation 1)

[0004]

(Equation 2)

[0005] Here, V _FR is the right front wheel speed, V _FL is the left front wheel speed, V _RR is the right rear wheel speed, and V _RL is the left rear wheel speed.

The wheel speed deviation value D is a rotation state value obtained from the wheel speeds of the four wheels, and is a variable given as a difference in the wheel speed ratio between the front and rear wheels in a diagonal relationship, for example. When the air pressure of such a tire decreases, it increases or decreases accordingly. The front and rear wheel speed ratio β is 4
This is a slip state value obtained from the wheel speed of the wheel, and represents a degree of a slip state generated in the drive wheel by the action of the driving force transmitted to the drive wheel. A smaller value indicates that the drive wheel is slipping.

When the tire air pressure of each wheel is a specified value, the wheel speed deviation value D becomes 0. However, when the tire air pressure of any of the four wheels falls below the specified value, the wheel speed deviation value D becomes zero. Since D increases or decreases, it is possible to detect a decrease in tire air pressure based on this.

However, for example, in a rear-wheel drive vehicle, when the tire air pressure of the right rear wheel, which is the driving wheel, falls below a specified value, the turning radius of the right rear wheel becomes small due to the decrease of the air pressure. Since the contact area becomes larger than the wheels and the force for suppressing the slip is increased, the other drive wheels are more likely to slip, and the wheel speed deviation value D varies depending on the degree of the slip state.

For this reason, as shown in FIG. 8A, the relationship between the front and rear wheel speed ratio β representing the degree of the slip state and the wheel speed deviation value D is regressed to a linear function using the least squares method. A regression line is obtained, and the wheel speed deviation value D is corrected to a value in an ideal running state in which no slip occurs (that is, the front-rear wheel speed ratio β = 1), thereby eliminating the influence of the slip of the drive wheels, thereby achieving accurate calculation. In addition, it is possible to detect a decrease in tire pressure.

[0010]

However, the above-mentioned conventional method is based on the premise that the wheel driving force always varies, such as when traveling on a flat road at a constant speed. When the variation in the wheel driving force decreases, the variation in the calculated wheel speed deviation value D and the front-rear wheel speed ratio β also decreases, and as shown in FIG. There is a possibility that the regression accuracy deteriorates and the wheel speed deviation value D is not accurately corrected. As a result, a problem that the detection accuracy of the air pressure decreases may occur.

In view of the above, an object of the present invention is to make it possible to accurately detect a decrease in tire air pressure even when the variation in driving force is small.

[0012]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a variation detecting means (3j) for detecting a variation in wheel driving force, and a variation in the rotational state value correcting means is provided. If the detecting means detects that there is variation in the wheel driving force, the rotation state value is corrected based on the current regression line calculated this time by the regression calculating means, and there is no variation in the wheel driving force. When this is detected, the rotation state value is corrected based on the regression line calculated last time by the regression calculation means.

As described above, when there is a variation in the wheel driving force, the rotation state is corrected by the current regression line obtained by the regression calculation means, and when there is no variation, the rotation state is corrected by the previous regression line. Is corrected. For this reason, even when the variation in the driving force is small, the rotation state value can be accurately corrected without a decrease in the regression accuracy due to a slight disturbance such as a slight turning, and a decrease in the tire air pressure can be accurately detected. .

The variation in the wheel driving force is, for example,
As described in claim 2, the detection can be performed based on the variation of the slip state value obtained by the slip state value calculation means.

As the slip state value, for example,
The front-rear wheel speed ratio (β) is given as a ratio of the wheel speeds of both rear wheels to the wheel speeds of both front wheels.

In this case, the front and rear wheel speed ratio calculated by the slip state value calculating means is stored by providing the front and rear wheel speed ratio storage means (3f).
The variation of the wheel driving force can be detected from the difference (Ep) between the maximum value and the minimum value of the front and rear wheel speed ratio stored in the front and rear wheel speed ratio storage means. If the difference between the maximum value and the minimum value of the speed ratio is larger than the first determination value (Ep * + Eth), it can be detected that there is variation in the wheel driving force.

In the present invention, when the predetermined time (Cth) elapses without updating the slip deviation value stored in the slip deviation value storage means, the variation detecting means is smaller than the first determination value. The second determination value (E
th ') is set, and when the difference between the maximum value and the minimum value of the front and rear wheel speed ratios is larger than the second determination value, it is detected that there is variation in the wheel driving force. And

In this way, it is possible to prevent the slip deviation value from being updated for a long time, and to prevent the tire pressure from being detected based on data that has been long before. As a result, it is possible to more accurately detect the current state of tire pressure reduction.

According to a seventh aspect of the present invention, the regression calculating means obtains a slip deviation value (A) represented by an amount of change in the wheel speed deviation value with respect to the front and rear wheel speed ratio, and the rotation state value correction means. Is characterized by correcting the rotation state value obtained by the rotation state value calculation means based on the slip deviation value. Thus, the rotation state value can be corrected based on the slip deviation value.

In this case, there is provided a slip deviation value storage means for storing the slip deviation value obtained by the regression calculation means, and the variation of the wheel driving force obtained by the variation detection means is a predetermined value. If it is larger than the determination value (Ep * + Eth), the slip deviation value previously stored in the slip deviation value storage means is updated to the current slip deviation value calculated by the regression calculation means, and the slip deviation Based on the slip deviation value stored in the value storage means, the rotation state value calculated by the rotation state value calculation means is corrected.

According to the ninth aspect of the present invention, the ideal running state value calculating means (3i) calculates an ideal state value (βid = F (A)) corresponding to a slip state value in an ideal running state without slip. The rotation state value correction means calculates the rotation state value in the ideal running state from the regression line calculated by the regression calculation means and the ideal state value calculated by the ideal running state calculation means. It is characterized by having.

As described above, the rotation state value in the ideal traveling state can be obtained from the regression line and the ideal state value, and based on the rotation state value in the ideal traveling state,
It is possible to accurately determine a decrease in tire air pressure.

The reference numerals in parentheses of the above means indicate the correspondence with specific means described in the embodiments described later.

[0024]

(First Embodiment) FIG. 1 shows a schematic configuration of a tire pressure detecting device according to an embodiment of the present invention. The tire pressure detecting device will be described with reference to FIG.

The tire air pressure detecting device detects that the air pressure of one of the tires of each wheel has decreased, and when the decrease of the tire air pressure is detected, the driver is warned to that effect. . The tire pressure detection device is mounted on a front-wheel drive or rear-wheel drive vehicle. In the present embodiment, a case where the tire pressure detection device is mounted on a rear-wheel drive vehicle will be described as an example.

The tire pressure detecting device is provided for each wheel 1 of the vehicle.
Wheel speed sensors 2a, 2b, 2c, 2d as wheel speed detecting means provided corresponding to a, 1b, 1c, 1d
And an arithmetic processing unit 3 to which detection signals from the wheel speed sensors 2a to 2d are input, and an alarm unit 4 for warning a driver of a decrease in tire air pressure based on a warning signal from the arithmetic processing unit 3. It is configured.

Of the wheel speed sensors 2a to 2d, two wheel speed sensors 2a and 2b are driven wheels (front right wheel and front left wheel).
1a and 1b are detected, and the remaining 2
The two wheel speed sensors 2c and 2d detect wheel speed signals in driving wheels (right rear wheel and left rear wheel) 1c and 1d.

The arithmetic processing unit 3 is composed of a microcomputer or the like, and performs various arithmetic operations based on detection signals input from the wheel speed sensors 2a to 2d. This arithmetic processing device 3 is configured as follows.

The arithmetic processing unit 3 includes a wheel speed calculating unit 3a as wheel speed calculating means, a wheel speed deviation value processing unit 3b
Is provided. The wheel speed calculator 3a calculates the wheel speed of each of the wheels 1a to 1d based on detection signals (for example, pulse signals) from the wheel speed sensors 2a to 2d. The wheel speed deviation value processing unit 3b includes a wheel speed deviation value calculation unit as a rotation state value calculation unit, a first wheel speed deviation value storage unit, and a wheel speed deviation value average processing unit. Various processes relating to the wheel speed deviation value D are performed based on the calculation result in the wheel speed calculation unit 3a.

In these configurations, first, the wheel speeds of the wheels 1a to 1d are calculated by the wheel speed calculator 3a based on the detection signals from the wheel speed sensors 2a to 2d. For example, the wheel speeds V _FL , V _FR , V _RL , and V _{RR of} each wheel are calculated from the number of detection signals from the wheel speed sensors 2a to 2d input within a few ms. Next, when the wheel speed is calculated, the wheel speed deviation value D shown in Equation 1 is calculated by the wheel speed deviation value calculation unit based on the data on the wheel speed. Then, data relating to the calculation result is stored in a memory provided in the first wheel speed deviation value storage unit, and the average value D of the wheel speed deviation values D is processed by the wheel speed deviation value averaging unit based on the stored contents. _AVE is required. The average value D _AVE of the wheel speed deviation values D is represented by the following equation, and corresponds to an average of n ₀ wheel speed deviation values D.

[0031]

(Equation 3)

The arithmetic processing unit 3 includes a front and rear wheel speed ratio processing unit 3c. The front and rear wheel speed ratio processing unit 3c includes a front and rear wheel speed ratio calculation unit as a slip state value calculation unit, a front and rear wheel speed ratio storage unit, and a front and rear wheel speed ratio average processing unit. In the front / rear wheel speed ratio processing unit 3c, after the front / rear wheel speed ratio β shown in Expression 2 is calculated by the front / rear wheel speed ratio calculation unit based on the data on the wheel speed sent from the wheel speed calculation unit 3a, Data relating to this calculation result is stored in a memory provided in the front-rear wheel speed ratio storage unit, and the front-rear wheel speed ratio average processing unit calculates an average value β _AVE of the front-rear wheel speed ratio β based on the stored contents. ing. The average value β _AVE of the front-rear wheel speed ratio β is expressed by the following equation: n ₀
This is equivalent to averaging the front-rear wheel speed ratio β.

[0033]

(Equation 4)

The arithmetic processing unit 3 is provided with a slip deviation value operation unit 3d, an ideal running state value operation unit 3e, a regression accuracy processing unit 3f, and a wheel speed deviation value correction processing unit 3g.

In the slip deviation value calculation section 3d, the wheel speed deviation value D calculated by the wheel speed deviation value calculation section in the wheel speed deviation value processing section 3b is compared with the front and rear wheel speed ratio processing section 3d.
The slip deviation value A is calculated based on the front-rear wheel speed ratio β calculated by the front-rear wheel speed ratio calculation unit in c. The slip deviation value A corresponds to a change amount (ΔD / Δβ) of the wheel speed deviation value D with respect to the front and rear wheel speed ratio β, and is based on n ₀ wheel speed deviation values D and the front and rear wheel speed ratio β. Is calculated using the least squares method. Note that the slip deviation value calculator 3d corresponds to a regression calculator.

The ideal running state value calculator 3e calculates the ideal running state value βid based on the calculation result in the slip deviation value calculator 3d. The ideal running state value βid is
This is equivalent to the front-rear wheel speed ratio β in an ideal running state without slip as a correction reference, and is calculated as a function of the first order or higher of the slip deviation value A. That is, the ideal running state value βid is represented by βid = F (A). For example, when the ideal running state value βid is a linear function of the slip deviation value A, βid = F (A)
1−Coef × | A | Here, Coef is a constant.

The regression accuracy processing unit 3f uses the contents stored in the front and rear wheel speed ratio storage unit in the front and rear wheel speed ratio processing unit 3c as an operation for calculating a wheel speed deviation correction value D' _{AVE to be} described later. The slip deviation value AA is calculated.
Specifically, the regression accuracy is evaluated from the stored front-rear wheel speed ratio β, and if the regression accuracy can be improved, the slip deviation value A obtained this time is stored as the slip deviation value AA to improve the regression accuracy. If it is not possible, a process is performed in which the previously obtained slip deviation value A (corresponding to a deviation stock value A * described later) is stored as it is as the slip calculation value AA. The regression accuracy evaluation here is performed, for example, based on whether or not the difference Ep between the stored maximum value and minimum value of the front and rear wheel speed ratio β is larger than a predetermined determination value Ep * + Eth. The regression accuracy processing section 3j functions as a variation detecting means for detecting a variation in the wheel driving force and a slip deviation value storage means for storing the slip deviation value A.

The wheel speed deviation correction unit 3g has a wheel speed deviation correction unit and a second wheel speed deviation storage unit. The wheel speed deviation value correction unit corresponds to a rotation state value correction unit. In this wheel speed deviation value correction unit, the wheel speed deviation average value D _AVE calculated by the wheel speed deviation value average processing unit in the wheel speed deviation value processing unit 3b and the front and rear wheels in the front and rear wheel speed ratio processing unit 3c. The front / rear wheel speed ratio average value β _AVE calculated by the speed ratio average processing unit and the regression accuracy processing unit 3
Based on the slip deviation value AA stored as f and the ideal traveling state value βid computed by the ideal traveling state value computing unit 3e, a corrected wheel speed deviation value D' _AVE is computed.
The corrected wheel speed deviation value D' _AVE corresponds to the wheel speed deviation value D in an ideal running state. Specifically, the corrected wheel speed deviation value D' _AVE is obtained as in the following equation.

[0039]

(Equation 5)

Then, in the second wheel speed deviation value storage unit,
The reference value D ' _AVE std of the corrected wheel speed deviation value D' _AVE calculated by the wheel speed deviation value correction unit is stored in the memory. The reference value D ′ _AVE std is a corrected wheel speed deviation value D ′ _AVE at the time of equal pressure of the four wheels, which is a reference for determining the air pressure. The wheel speed deviation calculated first after the operation of the arithmetic processing unit 3. value D and the front and rear wheel speed ratio beta from the obtained wheel speed deviation mean D _{AV E,} longitudinal wheel speed ratio average value beta _AVE,
This corresponds to a value calculated from the slip deviation value A and the ideal running state value βid.

Further, the arithmetic processing unit 3 is provided with a differential pressure determination value calculation section 3h and an air pressure drop determination section 3i. In the differential pressure determination value calculation section 3h, the reference value D ' _AVE std stored in the second wheel speed deviation value storage section in the wheel speed deviation value correction processing section 3f and the correction obtained by the wheel speed deviation value correction section. A differential pressure determination value ΔD ′ _AVE is determined based on the rear wheel speed deviation value D ′ _AVE . This differential pressure determination value ΔD ′ _AVE is
The difference (ΔD ′ _AVE = D ′ _AVE std−D ′ _AVE ) between the reference value D ′ _AVE std and the wheel speed deviation value D ′ _AVE, and the differential pressure determination value ΔD ′ _AVE is used to evaluate the decrease in air pressure. Used for

In the air pressure drop judging section 3i, the differential pressure judgment value Δ
The air pressure determination is performed by comparing the absolute value | ΔD ′ _AVE | of D ′ _AVE with a preset threshold value Dsh. Specifically, if the absolute value | ΔD ′ _AVE | is larger than the threshold value Dsh, a warning signal indicating that the tire air pressure is decreasing is sent to the warning device 4.

When the warning signal indicating that the tire air pressure is low is input, the warning device 4 turns on the warning lamp provided in the vehicle interior, for example. It warns that the air pressure has dropped.

Next, FIGS. 2 and 3 show flowcharts of the tire air pressure determining process by the tire air pressure detecting device having the above configuration, and the details of the tire air pressure determining process will be described with reference to these drawings.

First, in step S100, the number of operations N is reset to N = 0. And step S
In 101, as a wheel speed calculation process based on detection signals from the wheel speed sensors 2a to 2d, a wheel speed calculation unit 3a
After calculating the wheel speeds V _FL , V _FR , V _RL , and V _RR of each wheel, the number N of wheel speed calculations is incremented. This processing is performed by calculating an average value of the wheel speed every few seconds for each wheel based on a wheel speed pulse of several seconds, for example.

In the following step S102, as a wheel speed deviation value calculation process, a wheel speed deviation value D is calculated by a wheel speed deviation value calculation section in the wheel speed deviation value processing section 3b. The wheel speed deviation value D is obtained by substituting each wheel speed obtained in step S101 into the above equation (1).
Then, in step S103, the wheel speed deviation value D stored so far in the memory of the first wheel speed deviation value storage unit.
(N) is one of the wheel speed deviation values D calculated this time.
Is stored. Incidentally, D (N) is an array of the wheel speed deviation value D n ₀ pieces of, so that the wheel speed deviation value D n ₀ or stored, stores the wheel speed deviation D in locations that match the number of calculations N It has become. And n ₀ wheel speed deviation values D
Is stored, for example, when the number of calculations N is reset to 0 in the counter reset process (step S100), the wheel speed deviation value D stored at a location corresponding to the number of calculations N is calculated for the newly calculated wheel. The speed deviation value D is appropriately updated.

In the following step S104, the front-rear wheel speed ratio β is calculated by the front-rear wheel speed ratio calculation unit in the front-rear wheel speed ratio processing unit 3c as the front-rear wheel speed ratio calculation process. The front and rear wheel speed ratio β is also obtained by substituting each wheel speed obtained in step S101 into the above equation (2).
Then, in step S105, the front-rear wheel speed ratio β stored so far in the memory of the front-rear wheel speed ratio storage unit is used.
As one of (N), the front-rear wheel speed ratio β calculated this time
Is stored. Incidentally, beta (N) is an array of longitudinal wheel speed ratio beta of the n ₀ pieces of the front and rear wheel speed ratio beta n ₀ or stored, to store the longitudinal wheel speed ratio beta in locations that match the number of calculations N It has become. And n ₀ front-rear wheel speed ratios β
Is stored, as in the case of D (N) described above, the data is updated to the newly calculated front and rear wheel speed ratio β as appropriate.

Thereafter, in step S106, the number of operations N
Is greater than or equal to n ₀ . If an affirmative determination is made, the process proceeds to step S107 assuming that the n ₀ wheel speed deviation values D and the front and rear wheel speed ratios β are stored, and if a negative determination is made, the process returns to step S101.

In the following step S107, a slip deviation value A is obtained by the slip deviation value calculation section 3d as a slip deviation value calculation process. That is, using the least squares method, a regression line is derived by regressing the relationship between the n ₀ front-rear wheel speed ratio β and the wheel speed deviation value D to a linear function, and the slip deviation value A is calculated from the slope of the regression line. Ask. The slip deviation value A indicates the dependence of the wheel speed deviation value D on the front-rear wheel speed ratio β.

[0050] Subsequently, in step S108, the wheel speed deviation averaging process, calculates the average value D _{AV E} of the wheel speed deviation D in the wheel speed deviation averaging processor of the wheel speed deviation value processing unit 3b. This average value D _AVE is calculated in step S10.
The wheel speed deviation value D for n ₀ stored in the above equation (3) is calculated by the above equation (3).
Is obtained by substituting into

In step S109, the average value β of the front-rear wheel speed ratio β is calculated by the front-rear wheel speed ratio average processing unit in the front-rear wheel speed ratio processing unit 3c.
Calculate _AVE . This average value β _AVE is calculated in step S105.
Is obtained by substituting the front and rear wheel speed ratios β for n ₀ stored in the above _equation into the above _equation (4).

In step S110, the ideal traveling state value computing section 3i computes an ideal traveling state value βid as an ideal traveling state value computing process. This ideal running state value βid is obtained from a first-order or higher-order function relating to the slip deviation value A calculated in step S110.

In step S111, a regression accuracy evaluation value determination process is performed. This regression accuracy evaluation determination processing is performed by the regression accuracy processing unit 3f. Details of the regression accuracy evaluation determination processing will be described based on the flowchart shown in FIG.

First, in step S201, as a regression accuracy evaluation value calculation process, the regression accuracy processing unit 3e stores the front and rear wheel speed ratio β stored in the front and rear wheel speed ratio storage unit in the front and rear wheel speed ratio processing unit 3c. The difference E between the maximum and minimum values of
Calculate p. By this processing, the variation in the front and rear wheel speed ratio β can be obtained. This difference Ep corresponds to a reference value for determining whether or not the wheel driving force varies.

In the following step S202, it is determined whether or not the difference stock value Ep * of the difference Ep has been stored, that is, whether or not the difference Ep has been calculated even once.
If a negative determination is made here, the process proceeds to step S203, in which the calculated difference Ep is stored as a difference stock value Ep *, and the slip deviation value A calculated in step S107 is stored as a difference value stock value A *. Keep it.

On the other hand, if a positive determination is made, step S204
The difference Ep changes the difference stock value Ep * to the threshold value E.
It is determined whether or not it is greater than a determination value Ep * + Eth to which th has been added. That is, there is a correlation between the variation in the wheel driving force and the variation in the front-rear wheel speed ratio β. ), The presence or absence of a variation in the wheel driving force is detected.

When the wheel driving force varies and when there is no variation, the wheel speed deviation value D and the front-rear wheel speed ratio β in each situation are plotted as shown in FIGS. 5 (a) and 5 (b).
It is represented as As can be seen from these figures, when there is some variation in the wheel driving force, the error range of the slope of the regression line becomes smaller as indicated by the arrow in the figure, and when the variation in the wheel driving force is small, the regression line becomes smaller. The error range of the inclination of the straight line increases as indicated by the arrow in the figure. From this, it can be said that the reliability of the slip deviation value A obtained when there is some variation in the wheel driving force is high, and the reliability of the slip deviation value A obtained when there is no variation in the wheel driving force is very small. Not very expensive.

For this reason, in the situation where a negative determination is made in step S204, there is no variation in the wheel driving force, and the reliability of the slip deviation value A obtained at this time cannot be said to be very high. If so, step S20
Proceeding to 5, the value stored as the deviation stock value A * is stored as the slip deviation value AA used for calculating the wheel speed deviation correction value D' _AVE .

On the other hand, a situation in which an affirmative determination is made is considered to have a certain degree of variation in the wheel driving force, and the reliability of the slip deviation value A obtained at this time is considered to be high. Proceeding to step S206, the slip deviation value A obtained this time is changed to the wheel speed deviation correction value D '.
_The difference Ep is stored as a new difference stock value Ep * while the difference Ep obtained this time is stored as the slip deviation value AA used for the calculation of _AVE .

Then, the process proceeds to a step S207, where the slip deviation value AA set in the step S205 or S206 is stored as a deviation value stock value A *, and the regression accuracy evaluation judging process ends.

Subsequently, in step S112, the wheel speed deviation correction unit in the wheel speed deviation correction unit 3g performs steps S108 to S11 as the wheel speed deviation correction processing.
The corrected wheel speed deviation value is obtained by substituting the wheel speed deviation average value D _AVE , the front and rear wheel speed ratio average value β _AVE , the ideal running state value βid, and the slip deviation value AA obtained in 1 into the above equation (5). _Find D ' _AVE .

FIG. 6 shows the corrected wheel speed deviation value D '.
_AVE , the slip deviation value A used to derive the corrected wheel speed deviation value D' _AVE , the ideal running state value βid, the wheel speed deviation average value D _AVE , and the front-rear wheel speed ratio average value β
The correlation of _AVE is shown, and these relationships will be specifically described.

FIG. 6 shows the correlation between the wheel speed deviation value D and the front / rear wheel speed ratio β when the tire pressure of one of the drive wheels 1c and 1d, here the left rear wheel, decreases. In this figure, white circles indicate the relationship between the calculated wheel speed deviation values D for n ₀ and the front and rear wheel speed ratio β,
A black circle indicates the relationship between the wheel speed deviation average value D _AVE and the front-rear wheel speed ratio average value β _AVE .

When the tire pressure of the left rear wheel, one of the drive wheels 1c and 1d, decreases, the wheel speed V _RL of the left rear wheel is reduced.
Increases, the front-rear wheel speed ratio β drops below 1 with a decrease in tire air pressure. Then, in the ideal running state, the ideal running state value βid is βid = F
(A). Therefore, as shown in step S113 of the present embodiment, based on the slip deviation value A,
An ideal running state value βid is obtained from the relationship βid = F (A).

On the other hand, as shown in step S107,
Using the least squares method, it is possible to derive a regression line obtained by regressing the relationship between the front and rear wheel speed ratios β for n ₀ and the wheel speed deviation value D into a linear function.

Therefore, as shown in step S112, the derived regression line and the ideal running state value βid = F
By determining the intersection with (A), the driving wheels 1c, 1d
The wheel speed deviation value D in an ideal running state when the air pressure drops, that is, the corrected wheel speed deviation value D' _AVE , can be obtained.

In this manner, the corrected wheel speed deviation value D' _AVE , which is the wheel speed deviation value D in an ideal running state when the air pressure of the drive wheels 1c and 1d is reduced, can be accurately obtained.

Then, in step S113, the reference value D '
It is determined whether _AVE std has already been detected.
This is determined by whether or not the reference value D ' _AVE std is stored in the memory of the second wheel speed deviation value storage unit in the wheel speed deviation value correction processing unit 3g. If the corrected wheel speed deviation value D ' _AVE calculated this time is the first value obtained after the operation of the arithmetic processing unit 3, the reference value D' _AVE std is not stored.
14, the D ' _AVE calculated this time is set to the reference value D' _{A VE} s
It is stored in the memory as td, and the process returns to step S100.
In addition, the corrected wheel speed deviation value D ′ calculated this time.
_{If AVE} is not the one obtained first, step S1
Proceed to 15.

In the following step S115, as the differential pressure determination value calculation processing, the reference value D 'is calculated by the differential pressure determination value calculation unit 3h.
_A differential pressure determination value ΔD ′ _AVE which is a difference between the _AVE std and the corrected wheel speed deviation value D ′ _AVE is obtained.

In step S116, the absolute value | ΔD ' _AVE | of the differential pressure determination value ΔD' _AVE is compared with a preset threshold value Dsh, and the absolute value | ΔD '
_It is determined whether or not _AVE | is greater than threshold value Dsh.

Thus, if an affirmative determination is made, step S
The program proceeds to 117, where it is determined that the tire air pressure has decreased, a warning signal to that effect is sent to the alarm device 4, and if a negative determination is made, the process is terminated and the process returns to step S101. Through the above processing, it can be determined whether or not the tire air pressure at each of the wheels 1a to 1d has decreased.

As described above, in the regression accuracy evaluation value determination processing, it is determined whether or not the wheel driving force varies based on the difference Ep between the maximum value and the minimum value of the front and rear wheel speed ratio β. I have. Then, the slip value A calculated when the variation in the wheel driving force is small is not used in the calculation of the wheel speed deviation correction value D' _AVE , and in that case, it is calculated before the variation in the wheel driving force becomes small. The slip value A is used as a slip value AA used for calculating the wheel speed deviation correction value D' _AVE . For this reason, even when the variation of the driving force is small, the wheel speed deviation value D can be accurately corrected without the regression accuracy being deteriorated by a slight disturbance such as a slight turning, and the tire pressure can be accurately reduced. Can be detected.

When traveling on a general road, it is considered that the period during which the variation in the wheel driving force is small is sufficiently smaller than the period during which the tire air pressure is reduced. Is used as the slip value AA used for calculating the wheel speed deviation correction value D' _AVE , it is possible to detect a decrease in tire air pressure without any problem.

In the prior art, the wheel speed deviation value D is corrected by setting the reference value for determining an ideal running state to the front and rear wheel speed ratio β = 1. Since the front and rear wheel speed ratio β does not become 1, overcorrection occurs. In such a case, the amount of change in the wheel speed deviation value D with respect to the decrease in tire air pressure differs depending on the driving wheel and the rolling wheel (follower wheel), and the pressure alerted when the tire air pressure decreases varies.

However, in the tire pressure detecting device according to the present embodiment, the slip deviation value A is obtained based on the wheel speed deviation value D and the front and rear wheel speed ratio β, and from this slip deviation value A, the ideal running state value βid = F The wheel speed deviation value D is corrected based on (A). For this reason, the corrected wheel speed deviation value D 'which is the wheel speed deviation value D in an ideal running state when the air pressure of the drive wheels 1c and 1d is reduced.
_AVE can be determined accurately without overcorrection.

Therefore, the variation of the corrected wheel speed deviation value D' _AVE coincides with that of the driving wheel and the driven wheel, and it is possible to prevent variations in the alarmed pressure when the tire air pressure drops.

(Second Embodiment) In this embodiment, the method of the regression accuracy evaluation value judgment processing is changed from that of the first embodiment. In addition, since the basic configuration of the tire pressure detection device in the present embodiment is the same as that of the first embodiment,
Only the regression accuracy evaluation determination processing will be described.

FIG. 7 shows a flowchart of the regression accuracy evaluation value judgment processing executed by the tire air pressure detecting device according to the present embodiment, and the details of the regression accuracy evaluation judgment processing will be described with reference to FIG.

First, in step S301, the same processing as step S201 in the first embodiment is performed, and the difference Ep between the maximum value and the minimum value of the front-rear wheel speed ratio β stored in the front-rear wheel speed ratio storage unit 3f is obtained. Is calculated.

In the following step S302, it is determined whether or not the count value of a counter (not shown) provided in the arithmetic processing unit 3 is larger than a predetermined threshold value Cth. Thus, it is determined whether a predetermined period (= threshold value Cth) has elapsed since the deviation value stock value A * was updated.

If a negative determination is made here, step S30
Proceeding to 3, it is determined whether or not the difference stock value Ep * has been stored as the same processing as step S202 in the first embodiment. If a negative determination is made in step S303, the process proceeds to step 304, in which the calculated difference Ep is stored as a difference stock value Ep *, as in step S203 in the first embodiment, and calculated in step S107. The obtained slip deviation value A is stored as a deviation value stock value A *. Conversely, if a negative determination is made in step S303, the process proceeds to step S305.

In step S305, as a process similar to step S204 in the first embodiment, it is determined whether or not the difference Ep is larger than a determination value Ep * + Eth. At this time, if a negative determination is made, the process proceeds to step S306 to increment the count value of the counter, and then proceeds to step S307. As a process similar to step S205 of the first embodiment, the value is stored as the deviation value stock value A *. Is stored as the slip deviation value AA. vice versa,
If an affirmative determination is made, the process proceeds to step S308, in which the slip deviation value A obtained this time is stored as the slip deviation value AA and the difference Ep obtained this time is stored as a process similar to step S206 of the first embodiment. It is stored as a new difference stock value Ep *.

On the other hand, if an affirmative determination is made in step S302, the flow advances to step S309 to determine whether the difference Ep is greater than a threshold value Eth '. The threshold value Eth 'used at this time is determined by a judgment value Ep *
A value smaller than + Eth is set. If an affirmative determination is made here, the process proceeds to step S310 to reset the count value of the counter to 0, and then proceeds to step S308, where the slip deviation value A obtained this time is stored as the slip deviation value AA. Difference Ep
Is stored as a new difference stock value Ep *. vice versa,
If a negative determination is made, the process proceeds to step S311, and the value stored as the deviation value stock value A * is stored as the slip deviation value AA, as in step S307.

Then, the flow proceeds to step S312, where the slip deviation value AA set in step S307, S308 or S311 is stored as the deviation value stock value A *, and the regression accuracy evaluation determination processing ends.

As described above, if an affirmative determination is made in step S305, the deviation value stock value A * is updated to the slip deviation value A obtained this time (steps S308 and S312). If the deviation stock value A * has not been updated even after the lapse of the predetermined period, the difference Ep is compared with the threshold value Eth '(step S309), and the difference Ep is set to the threshold value Et.
When h is larger than h ′, that is, when it is assumed that the variation in the wheel driving force is acceptable to some extent, the deviation stock value A * is updated to the slip deviation value A obtained this time. Has become.

Therefore, it is possible to prevent the long-term deviation value stock value A * from being updated, and prevent the tire pressure from being detected based on the data obtained a long time ago. As a result, it is possible to more accurately detect the current state of tire pressure reduction.

(Other Embodiments) In each of the above embodiments, an example in which one embodiment of the present invention is applied to a rear wheel drive vehicle has been described. However, the present invention may be applied to a front wheel drive vehicle. . In this case, the relationship is such that the ideal running state value βid becomes greater than 1 as the tire pressure of the drive wheel decreases.

In the above description, the wheel speed deviation value D shown in Equation 1 is used as the rotation state value.
Others may be used. That is, the rotation state value is
Any value may be used as long as the wheel speed of each of the wheels 1a to 1d is related so that the deviation of the wheel speed between the left and right wheels that may occur due to the vehicle turning is canceled out. For example, there are the following.

[0089]

(Equation 6)

[0090]

(Equation 7)

[0091]

(Equation 8)

All of these relational expressions are caused by the turning of the vehicle by taking the respective differences between the left and right front wheels and between the right and the front right wheels, where similar wheel speed deviations may occur during turning of the vehicle. The wheel speeds of the wheels 1a to 1d are associated with each other so that the deviation of the wheel speed between the left and right front wheels and between the left and right rear wheels is canceled.

As described in the above embodiment, when the system warns of a decrease in tire air pressure when the wheel speed deviation value D exceeds a predetermined threshold value, the slip deviation value (slope) A Is small, the wheel speed deviation value D due to slip need not be corrected. This is a problem even if there is some error since the wheel speed deviation value D may not exceed the threshold value when the slip deviation value A is small when the rear wheels (drive wheels) are depressurized. This is because the inclination A becomes almost zero in any case when the front wheel (rolling wheel) is depressurized, so that it is not necessary to correct the wheel speed deviation value D due to slip. Therefore, by excluding the case where the slip deviation value A is small from the correction target, it is possible to exclude the case where the necessity of the correction during the rear wheel depressurization and the case where the front wheel depressurization is low from the correction target.

[0094] In the above embodiments, after the average value D _AVE of the wheel speed deviation D, Betaid the average value D _AVE
= F (A) to obtain the corrected wheel speed deviation value D ′ _AVE by projecting the curve on the curve represented by F = (A). Each of the wheel speed deviation values D is represented by βid = F (A). After projecting on a curved line, an average value thereof may be taken.

In each of the above embodiments, each time the number of operations N reaches n ₀ , the wheel speed deviation values D and the front-rear wheel speed ratio β for n ₀ data stored up to that point are calculated.
The average value D _AVE and the average value β _AVE are obtained, and the absolute value | ΔD ′ _{A VE} | of the differential pressure determination value ΔD ′ _AVE is obtained. However, in such a case, the tire air pressure determination cannot be performed while n ₀ data is accumulated. For this reason, in the wheel speed deviation value storage unit and the front and rear wheel speed ratio storage unit, the oldest stored wheel speed deviation value D and front and rear wheel speed ratio β are newly calculated wheel speed deviation value D and front and rear wheel speed ratio. β is updated as appropriate, and the average value D _AVE and the average value β _AVE are calculated every time the value is updated, so that the tire air pressure can be determined every short time.

In each of the above embodiments, the case where the rotation state value (wheel speed deviation value D) is corrected based on the ideal traveling state value βid = F (A) has been described as an example. In a method that adopts a method of correcting the rotation state value, the regression accuracy evaluation value determination processing described in each embodiment can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a tire pressure detecting device according to a first embodiment of the present invention.

FIG. 2 is a flowchart of control executed by the tire pressure detecting device shown in FIG.

FIG. 3 is a flowchart of control executed by the tire pressure detecting device following FIG. 2;

FIG. 4 is a flowchart of a regression accuracy evaluation value determination process shown in FIG. 3;

FIG. 5 shows a case where there is a variation in wheel driving force and a case where there is no variation.
It is the figure which plotted the wheel speed deviation value D and the front-rear wheel speed ratio (beta) in each situation.

6 is a diagram showing the relationship between the wheel speed deviation mean D _{AV E} before correction in the tire air pressure detecting device and the corrected wheel speed deviation D _'AVE shown in FIG.

FIG. 7 is a flowchart of a regression accuracy evaluation value determination process executed by the tire air pressure detection device according to the second embodiment of the present invention.

FIG. 8A is a diagram showing a relationship between a wheel speed deviation value D before correction and a wheel speed deviation value D ′ after correction in a conventional tire pressure detecting device, and FIG. FIG. 7 is a diagram illustrating regression accuracy when a slight disturbance such as a fine turn occurs when there is no variation in force.

[Explanation of symbols]

1a to 1d: wheels, 2a to 2d: wheel speed sensors, 3 ...
Arithmetic processing unit, 3a: wheel speed calculating unit, 3b: wheel speed deviation value processing unit, 3c: front and rear wheel speed ratio processing unit, 3d: slip deviation value calculating unit, 3e: ideal running state value calculating unit,
3f: regression accuracy processing section, 3g: wheel speed deviation value correction processing section, 3h: differential pressure determination value calculation section, 3i: air pressure drop determination section, 4 ... alarm device.

 ────────────────────────────────────────────────── ─── Continuing from the front page (71) Applicant 000000011 Aisin Seiki Co., Ltd. 2-1-1 Asahi-cho, Kariya-shi, Aichi (72) Inventor Motonori Tominaga 14 Iwatani, Shimoba-Kakucho, Nishio-shi, Aichi Japan Automotive Parts Co., Ltd. Within the Research Institute (72) Inventor Yuichi Inoue 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO Corporation (72) Inventor Masahiro Yoneya 1-Toyota-cho, Toyota-shi, Aichi Prefecture Inside Toyota Motor Corporation (72) Invention Person Kazuhiro Kamiya 2-1-1 Asahicho, Kariya City, Aichi Prefecture Inside Aisin Seiki Co., Ltd.

Claims (9)

[Claims] 1. Wheel speed detecting means (2a-2) for detecting the wheel speed of each wheel of a front-wheel drive or rear-wheel drive vehicle.
d, 3a) and the rotational state obtained by relating the wheel speeds detected by the wheel speed detecting means so as to cancel the deviation of the wheel speed between the left and right wheels caused by the turning of the vehicle. Rotation state value calculation means (3) for calculating the value (D)
b) a slip state value calculation means (β) that calculates a slip state value (β) depending on the degree of slip state between the drive wheel and the driven wheel based on the wheel speed detected by the wheel speed detection means. 3c) regressing the rotation state value calculated by the rotation state value calculation means and the slip state value calculated by the slip state value calculation means into a linear function to derive a regression line (3d) ), A rotation state value correction unit (3g) for correcting the rotation state value obtained by the rotation state value calculation unit based on the regression line obtained by the regression operation unit, A tire pressure drop determining means (3i) for determining a drop in tire pressure of each wheel based on the corrected rotation state value. I, variation detection means (3 for detecting the variation of the wheel driving force
f), wherein the rotation state value correcting means, based on the current regression line calculated this time by the regression calculating means, when the variation detecting means detects that there is a variation in the wheel driving force. When the rotation state value is corrected and it is detected that there is no variation in the wheel driving force, the rotation state value is corrected based on the regression line previously calculated by the regression calculation means. A tire pressure detecting device characterized in that the tire pressure is detected. 2. The system according to claim 1, wherein the variation detecting means detects the variation in the wheel driving force based on the variation in the slip state value obtained by the slip state value calculating means. 3. The tire pressure detecting device according to 1. 3. The front-rear wheel speed ratio (β) given as a ratio of a wheel speed of both rear wheels to a wheel speed of both front wheels as the slip state value.
3. The tire pressure detection according to claim 2, wherein the variation detection unit detects variation in the wheel driving force based on variation in the front-rear wheel speed ratio. 4. apparatus. 4. A front-rear wheel speed ratio storage means (3c) for storing a front-rear wheel speed ratio calculated by the slip state value calculation means, wherein the variation detecting means stores the front-rear wheel speed ratio storage means. The tire pressure detecting device according to claim 3, wherein the variation of the wheel driving force is detected from a difference (Ep) between the maximum value and the minimum value of the front and rear wheel speed ratios. 5. The variance detecting means determines a difference between a maximum value and a minimum value of the front-rear wheel speed ratio as a first determination value (Ep).
5. The tire pressure detecting device according to claim 4, wherein when it is larger than (+ Eth), it is detected that there is variation in the wheel driving force. 6. A slip deviation value (A) represented by a change amount of the wheel speed deviation value with respect to the front-rear wheel speed ratio is obtained by the regression calculation means, and the obtained slip deviation value is stored. A slip deviation value storage unit that, when the variation detection unit detects that the wheel driving force varies, the slip deviation value stored in the slip deviation value storage unit last time. Is updated to the current slip deviation value calculated by the regression calculation means. The variation detection means sets the slip deviation value stored in the slip deviation value storage means for a predetermined time (not updated). After Cth), a second determination value (Eth ′) smaller than the first determination value is set, and the maximum value of the front-rear wheel speed ratio is set. If the difference between the small value is greater than the second determination value, the tire air pressure detecting device according to claim 5, characterized in that is adapted to detect the variation of the wheel driving force is present. 7. The regression calculation means calculates a slip deviation value (A) represented by a change amount of the wheel speed deviation value with respect to the front-rear wheel speed ratio. The tire pressure detection device according to any one of claims 1 to 4, wherein the rotation state value obtained by the rotation state value calculation means is corrected based on the slip deviation value. 8. Slip deviation value storage means for storing a slip deviation value obtained by the regression calculation means, wherein the slip deviation value storage means comprises a variation in the wheel driving force determined by the variation detection means. Is larger than the predetermined determination value (Ep * + Eth), the slip deviation value previously stored in the slip deviation value storage means is updated to the current slip deviation value calculated by the regression calculation means. Wherein the rotation state value correction means corrects the rotation state value obtained by the rotation state value calculation means based on the slip deviation value stored in the slip deviation value storage means. The tire pressure detecting device according to claim 7, characterized in that: 9. An ideal state value (βid = Fid) corresponding to the slip state value in an ideal running state without slip.
(A)) and an ideal running state value calculating means (3i), wherein the rotation state value correcting means is provided with a regression line obtained by the regression calculating means and an ideal running state obtained by the ideal running state calculating means. The tire pressure detection device according to any one of claims 1 to 8, wherein a rotation state value in an ideal running state is obtained from the state value.